Impact resistance, fuel economy standards and structural rigidity are important fundamental concerns in automotive structural design. Fuel economy standards dictate the use of lighter materials. This usually translates into reducing the thickness of materials or using lighter weight material. Impact resistance dictates the use of thicker materials at least in localized areas. Structural rigidity also typically requires an increase of material.
The use of composite materials which are generally stronger and lighter than their metallic counterparts has increased over the years. The present inventor has pioneered a novel approach to structural part reinforcement through localized reinforcement of critical regions using microsphere-filled thermally expandable resins, such as: composite door beam which has a resin based core that occupies one-third of the bore of a metal tube; a hollow laminate beam characterized by high stiffness-to-mass ratio and having an outer portion which is separated from an inner tube by a thin layer of structural foam; a W-shaped carrier insert reinforcement which carries a foam body for use in reinforcing a hollow beam; a bulk head that utilizes a thermally expandable foam to provide localized reinforcement of a rail for the attachment of an engine cradle or the like.
Joints of an automotive vehicle are the weakest part of the structure. Stiffening the joint improves the overall stiffness in ride characteristics of the vehicle, In the formation of the automotive vehicle body, several structural/body panel members are welded or bonded together. The joints typically are hollow by their very nature. The hollow structure allows the flow of E-coat through the structural members to increase corrosion resistance. Various techniques have been used by automotive manufacturers to increase the rigidity of the joints of the vehicle. Typically, the solutions have involved substantially increasing the bulk, size and/or complexity of the joints to thereby increase rigidity. By increasing the bulk of the joints, precious packaging space has been reduced. Also, the weight of the structure due to its bulk has been increased.